At moderate risk of putting my foot in my mouth, not knowing your specific situation[1]: It sounds like the modelers did exactly what they were supposed to. J

At moderate risk of putting my foot in my mouth, not knowing your specific situation[1]: It sounds like the modelers did exactly what they were supposed to. Just because N2 isn't directly controlled doesn't mean [N2] isn't a valid factor - even if its only mechanistic action is as a diluent. Its entirely possible an aspect of a reaction is sensitive to absolute reactant partial pressures as opposed to just relative concentration. Just as often as modellers going nuts, abusing either the chemistry or signal-to-noise, I've also seen chemists argue that multivariate-modelling of some rather simple system is impossible or 'not science', relegating research to inefficient linear trial and error. [1] For instance, if that is a Fischer-Tropsch reactor you are describing, then yes [N2] would likely go up with higher yield as your reactive gas species coalesce into heavier molecules.